The present invention relates generally to a liquid spray head preferably used in a liquid spray recording apparatus and a production method thereof. In particular, the present invention relates to a liquid spray head having a piezoelectric element that pressurizes the liquid chamber and its production method.
Generally, liquid spray recording apparatuses employ a liquid spray head comprising a liquid chamber, nozzles, liquid paths and an ink supply system. Such apparatuses are utilized by applying energy to the ink filled in the liquid chamber causing the ink stored therein to be ejected out through the liquid paths. As a result of this ejection, ink drops are sprayed from the nozzles, whereby character and graphic information or the like is recorded on a recording medium. A means that pressurizes the chamber, by way of example, a piezoelectric element or a heater for heating the ink in the liquid chamber, is used to the apply energy to the ink.
Conventional liquid spray heads similar to that described above and components related thereto are discussed in Japanese Patent Publication No. 62-22790, Japanese Laid-Open Patent Application 2-219654, U.S. Pat. No. 4,312,008, Japanese Journal of Applied Physics, Vol. 30, No. 12B, December 1991, pp. 3562-3566 by Torii, et al., Japanese Patent Publication No. 4-43435, and Japanese Laid-Open Patent Application 3-124450.
Japanese Patent Publication No. 62-22790 relates to a production method for a liquid spray head that forms an electrode on a substrate, which is fabricated as a thin layer in a location corresponding to the liquid chamber. A lead zirconate titanate (PZT) thin film is formed at a location corresponding to the liquid chamber by a sputtering, printing or other thin-film formation techniques.
In Japanese Laid-Open Patent Application 2-219654, a liquid spray head is provided with liquid chambers and liquid paths formed on a thin plate laminated on a semiconductor substrate provided with nozzles. A diaphragm is laminated above the liquid chambers and a piezoelectric vibrator is provided on the top portion of the diaphragm. Japanese Laid-Open Patent Application 2-219654 also relates to a production method for a liquid spray head that forms nozzles on a semiconductor substrate. In such a method, a dry film is adhered on the semiconductor substrate, and a diaphragm, a lower electrode, a piezoelectric film and an upper electrode are laminated thereon. The dry film is then removed by conventional means to complete this process.
In U.S. Pat. No. 4,312,008, a liquid spray head is fabricated by providing liquid paths formed in a substrate surface and liquid chambers which pass through the substrate. A substrate is adhered to both surfaces of the substrate and a piezoelectric element is provided thereon.
The Torii, et al. reference merely relates to the use of platinum for the lower electrode of a PZT thin film.
In Japanese Patent Publication No. 4-43435, an electrode formation method for a piezoelectric thin film is discussed in which a metal thin film base and a platinum film are formed on an insulating thin film. The films are heated at a temperature that causes the surface of the platinum thin film to become uneven due to crystal grain growth.
In Japanese Laid-Open Patent Application 3-124450, submitted by the inventors of the present invention, a production method for a liquid spray head is disclosed in which nozzles are formed from one surface of a monocrystalline silicon substrate. As disclosed therein, a p-type monocrystalline silicon is grown by epitaxy and a piezoelectric element is formed on the other surface of the monocrystalline silicon substrate. The p-type silicon layer and the monocrystalline silicon substrate are then etched, and the liquid chambers, a cantilever and center type diaphragms are formed therein.
However, the above prior art liquid spray heads, their component elements and their production methods have various deficiencies, as explained hereinbelow.
In the Japanese Patent Publication No. 62-22790, it is clear that though the thickness of the component elements is not clearly specified, in the embodiments the thickness of the PZT, tp, is believed to be 50 xcexcm and the diaphragm thickness, tv, is believed to be from 50 to 100 xcexcm. Accordingly, it is apparent that Japanese Patent Publication No. 62-22790 could not teach or suggest that the sum of tp+tv should be less than about 10 xcexcm. However, if tp+tv is about 100 xcexcm, as suggest by this reference, the amount of deformation in the diaphragm when a voltage is applied to the PZT is small and inadequate to reliably eject ink from such a liquid spray head. This is a result of the thicknesses of the diaphragm and the PZT layer being too large. Thus, in order to sufficiently deform the volume of the liquid chamber to facilitate the spraying of liquid, a round liquid chamber with about a 2 mm diameter is said to be required. However, in order to increase the resolution in such an apparatus, a planar configuration results in which the liquid chamber pitch is greater than the nozzle pitch as described therein. Such an arrangement results in poor surface area utilization. That is, the planar size of a liquid spray head with seven nozzles is about 20 mmxc3x9715 mm. As such, if the number of nozzles is increased, not only does the planar size becomes larger, but the speed of the liquid spray operation decreases significantly because the liquid paths linking the liquid chambers and nozzles becomes longer and greatly increases the liquid path resistance.
Moreover, in a method for making such a liquid spray head, a thin diaphragm is fabricated at a position corresponding to the liquid chambers and a PZT layer is formed above the diaphragm. However according to experiments performed by the inventors, when tp+tv was made thinner than specified, e.g., tp substantially equal to 3 xcexcm and tv substantially equal to 1 xcexcm, and the PZT layer was formed after fabricating the liquid chambers and diaphragm, the liquid spray head exhibited sag, wrinkles, breaking, etc., during the production process. This resulted in significantly reduced production yields of the liquid spray head.
Referring to Japanese Laid-Open Patent Application 2-219654, the nozzles in this reference are formed by machining the planar oriented (100) Si substrate. For example, when the nozzles are formed by anisotropic etching of the (100) Si substrate to a thickness of about 300 xcexcm, even though the nozzle dimension is 30 xcexcm square, the angular relationship with the (111) surface which has a slow etching rate unavoidably results in an opening about 400 xcexcm square on the opposite substrate surface. Therefore, it is difficult to make the nozzle pitch less than 400 xcexcm and, thus, the highest resolution possible is only about 60 dots per inch (dpi). That is, it is impossible to increase the density of the nozzles on the liquid spray head in an apparatus according to Japanese Laid-Open Patent Application 2-219654.
Further, as discussed therein, the piezoelectric film and upper and lower electrodes are both larger than the liquid chambers. Accordingly, in such a configuration, it is difficult at best to efficiently deform the diaphragm and spray liquid when voltage is applied to the piezoelectric film. Also, this reference is silent as to the size or thickness of the piezoelectric film, the upper and lower electrodes and the liquid chambers required to efficiently spray liquid.
Finally, in Japanese Laid-Open Patent Application 2-219654, a single SiO2 layer is used as the diaphragm. As will be understood by one of ordinary skill in the art, SiO2 has a small Young""s modulus of approximately 1010 N/m2. Accordingly, when a piezoelectric thin film is formed above the SiO2 layer and the piezoelectric thin film is deformed laterally by applying a voltage, although it extends a fair distance laterally, its longitudinal deformation is not very great. That is, when one SiO2 layer is used as the diaphragm, it is impossible to efficiently deform the diaphragm and reliably spray liquid when voltage is applied to the piezoelectric film. Japanese Laid-Open Patent Application 2-219654 is silent regarding the diaphragm characteristics or material required for efficiently spraying a liquid.
U.S. Pat. No. 4,312,008, fails to discuss a configuration in which a piezoelectric crystal is affixed to the top of the diaphragm. U.S. Pat. No. 4,312,008 discusses an embodiment of attachment of the piezoelectric crystal by means of an indium-based solder. As is apparent, the piezoelectric element being used is thicker than disclosed in Japanese Patent Publication No. 62-22790. Therefore, as in Japanese Patent Publication No. 62-22790, the nozzles essentially cannot be fabricated with a sufficiently high enough density. U.S. Pat. No. 4,312,008 also discusses, when using anisotropic etching to form the liquid paths, that the path shape is determined by the surface orientation of the Si substrate and cannot be freely selected. For example, when (100) Si is used, the cross-sectional shape of the liquid path is an inverted triangle, while when (110) Si is used, the cross-sectional shape of the liquid path is rectangular. Such cross-sectional shapes have various deficiencies. More specifically, when the liquid path is an inverted triangle, bubbles readily build up which results in poor quality printing. On the other hand, if the liquid path is a rectangular, the depth is difficult to control, and deviations occur in the liquid spray characteristic.
Further, undercut etching unavoidably occurs where the liquid paths and liquid chambers intersect, which results in an irregular intersection and an inconsistent liquid spray characteristic. In addition to this, since two substrates for sealing the Si substrate and two attachment processes are required in this conventional example, the production process is more complicated and production costs are increased.
In Japanese Journal of Applied Physics, Vol. 30, No. 12B, December 1991, pp. 3562-3566, Torii, et al., a platinum film is formed directly on SiO2 as the lower electrode of the PZT film. However, in this type of configuration, it is well known that there is a problem with the bond between the silicon oxide and the platinum. Experiments conducted by the inventors confirmed that separation occurred between the silicon oxide and the platinum in heat treatment during or after PZT film formation or during operation after completion. Also, as discussed in Japanese Patent Publication 4-43435, it is known that titanium can be introduced between the platinum and the insulating material to improve the adherence between the silicon oxide or other insulating material and platinum and thereby solve the above problem. However, protrusions occur in the platinum surface in the heat treatment during or after formation of the PZT film and this lowers the breakdown voltage of the PZT film. As a result, spray heads fabricated in this fashion are somewhat more unreliable.
In Japanese Laid-Open Patent Application 3-124450 a configuration is shown in which the etching solution automatically circulates to the surface on the side facing the piezoelectric element when anisotropy etching of the monocrystalline silicon substrate is performed. This configuration results in side etching of the piezoelectric element by the anisotropic etching solution, e.g., potassium hydroxide aqueous solution, of the monocrystalline silicon substrate. Spray head fabricated in accordance with this process, have a lower yield.
It is an object of the present invention to provide a liquid spray head that obviates the aforementioned problems of the conventional liquid spray head.
It is a further object of the present invention to provide a method of producing liquid spray heads in accordance with the present invention.
It is another object of the to provide a spray head that facilitates efficient liquid spray operation and features planar compactness such that high nozzle density may be obtained even when the number of nozzles is increased.
It is still another object of the present invention to provided a liquid spray head that realizes a lower electrode with a low protrusion density on the surface and a PZT film having a high breakdown voltage for improving the liquid spray characteristics.
It is a further object of the present invention to provide a liquid spray head in which it easy to control the shape and depth of the liquid chambers and liquid paths, has no bubble buildup or deviation in the liquid spray characteristics, and increases the freedom of design.
It is still a further object of the present invention to provide a liquid spray head production method that achieves a high production yield even when a thin diaphragm and piezoelectric element are formed in order to realize a liquid spray head according to the present invention.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings.
Although the detailed description and annexed drawings describe a number of preferred embodiments of the present invention, it should be appreciated by those skilled in the art that many variations and modifications of the present invention fall within the spirit and scope of the present invention as defined by the appended claims.
According to an aspect of the present invention a liquid spray head is provided with a plurality of liquid spray elements arranged in an array on a substrate. Each element comprises a chamber arranged on the substrate for holding a liquid to be sprayed, a nozzle; a liquid path for communication with the nozzle and the chamber, a diaphragm arranged on the liquid chamber, a piezoelectric element comprising a lower electrode arranged on the diaphragm, a piezoelectric film comprising a lead zirconate titanate film arranged on the lower electrode and an upper electrode arranged on the piezoelectric film, and a means for applying energy to the piezoelectric element so as to bend the diaphragm for deforming a volume of the liquid chambers to spray the liquid. The liquid chambers have a pitch equal to the pitch of the nozzles, and the following relationships are satisfied:
10xe2x89xa6W/Lxe2x89xa6150xe2x80x83xe2x80x831)
tpxe2x89xa7tvxe2x80x83xe2x80x832)
0.012xe2x89xa6(tp+tv)/L less than 0.08xe2x80x83xe2x80x833)
where L is a length of the liquid chambers in an array direction, W is a length of the liquid chambers in a depth direction, tp is a thickness of the lead zirconate titanate film and tv is a thickness of the diaphragm.
By using this configuration, not only is the liquid spray efficiency superior, the nozzle density can be increased and the liquid spray head can be made more compact and integrated.
According to another aspect of the present invention, a configuration is employed in which the substrate on which the liquid chambers are formed is fabricated from planar oriented (110) monocrystalline silicon and the depth direction of the liquid chambers is in the  less than I12 greater than  or  less than I12 greater than  direction. By this means, the liquid chamber dimensions can be made more precise.
According to a further aspect of the present invention, the liquid spray is also configured such that the relationship between the upper electrode length Lu in the array direction of the liquid chambers, the PZT length Lp in the array direction of the liquid chambers, and the lower electrode length L1 in the array direction of the liquid chambers is
Luxe2x89xa6Lp less than L1
By this means, a piezoelectric element can be configured that avoids problems in the production process and suppresses leakage current.
According to an additional aspect of the present invention, the liquid spray head is also configured such that the length L in the array direction of the liquid chambers and the length Lu of the upper electrode in the array direction of the liquid chambers have the relationship
L greater than Lu
Since this makes it possible to efficiently deform the diaphragm, liquid spray can be performed more efficiently than conventionally possible.
According to still another aspect of the present invention, the liquid spray head is also configured such that the relationship between the upper electrode length Wu in the depth direction of the liquid chambers, the PZT length Wp in the depth direction of the liquid chambers, the lower electrode length W1 in the depth direction of the liquid chambers and the depth direction length W of the liquid chambers is
W less than Wu less than Wp less than W1
By this means, problems are avoided in the production process and a piezoelectric element can be configured that suppresses leakage current. Further, leading an electrode from the upper electrode can be easily performed.
According to still a further aspect of the present invention, the liquid spray head is also configured such that the Young""s modulus of the diaphragm is greater than 1xc3x971011 N/m2. This increases the amount of deformation of the diaphragm and facilitates liquid spray operation with sufficient margin. More particularly, if the Young""s modulus of the diaphragm is greater than 2xc3x971011 N/m2, deformation of the diaphragm can be greatly increased and the length W in the depth direction of the liquid chamber can be reduced, whereby the liquid spray head can be made more compact and faster.
A suitable material for use as the diaphragm is one that contains one or two or more of silicon nitride, titanium nitride, aluminum nitride, boron nitride, tantalum nitride, tungsten nitride, zirconium nitride, zirconium oxide, titanium oxide, aluminum oxide, silicon carbide, titanium carbide, tungsten carbide or tantalum carbide as the principal component(s).
It is also desirable that the diaphragm be configured with a laminated structure comprising a material layer with a Young""s modulus of 1xc3x971011 N/m2 or greater (more desirably 2xc3x971011 N/m2 or greater) and a silicon oxide layer and that the silicon oxide layer be disposed at least above or below the material layer. By this means, adherence to the lower electrode or the substrate is strengthened, thus increasing production yield.
According to still an additional aspect of the present invention, a configuration is employed wherein a material layer containing aluminum oxide, zirconium oxide, stannic oxide, zinc oxide or titanium oxide as its principal component or a material layer containing two or more of the above materials as its principal components is inserted between the diaphragm and the lower electrode. This facilitates high temperature heat treatment and improves the piezoelectric characteristic of the PZT film.
According to yet another aspect of the present invention, the lower electrode may have a two-layer structure, wherein the layer in contact with the diaphragm is titanium and the layer in contact with the PZT is platinum or a platinum-containing alloy and the thickness of the titanium is less than 80 xc3x85. By this means, it is possible to improve the breakdown voltage of the PZT film.
According to yet a further aspect of the present invention, the first substrate, which comprises liquid chambers and diaphragms and piezoelectric elements formed in that order so they cover the openings of the liquid chambers, and the second substrate in which the liquid paths are formed are joined into a single unit so that the liquid chambers formed in the first substrate and the liquid paths formed in the second substrate are contiguous.
By this means, it is easy to control the shape and depth of the liquid paths and the shape of the intersections of the liquid paths and the liquid chambers can be made constant, thus raising the freedom of design while eliminating the causes of air bubbles and deviations in the liquid spray characteristic.
It is also desirable that a hydrophilic material be formed on the inside surfaces of the liquid chambers. By this means, when a water-based material is used as the liquid, the wetting characteristic between the liquid chambers and liquid paths and the liquid is improved and the generation of bubbles is reduced.
A configuration may also be employed wherein openings in the cross-section where the first substrate and the second substrate are joined are used as the nozzles. In accordance with such a configuration, the nozzle plate, which is normally an expensive separate part, can be eliminated. The nozzles may also be formed in the second substrate. Thus, the density of the nozzles can be advantageously increased.
According to still yet a further aspect of the present invention, a production method for forming a liquid spray head is provided comprising the step of forming a diaphragm on a first surface of a substrate. A piezoelectric element is formed by laminating a lower electrode, a piezoelectric film and upper electrode having a first surface arranged on the diaphragm, and a second surface of the piezoelectric element is protected. A liquid chamber is formed at a predetermined position on a second surface of the substrate.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.